The GNU C Library will be rebased in F21 to match glibc 2.20.

[Florian Weimer]

On 07/31/2014 07:41 PM, Josh Boyer wrote:
> To expand on this just a bit, the s/390 ABI break was done by the
> s/390 glibc port maintainers and was done intentionally.  This wasn't
> a "oops, we accidentally broke the ABI" bug.  It was something the
> s/390 maintainers decided was of minimal concern and it turns out they
> were wrong.

And we couldn't have avoided that if we used only released glibc 
versions in rawhide because the 2.19 release had the ABI change, too. 
It wasn't just in the git master branch.

-- 
Florian Weimer / Red Hat Product Security